Which is a requirement for the lining of a flank strap?

The requirement for the lining of a flank strap to be made of fleece or neoprene is significant due to the comfort and safety it provides for the horse. Fleece and neoprene are both materials that offer cushioning and help to prevent irritation or chafing against the horse's skin. This is particularly important in rodeo events where the flank strap is used, as it needs to apply pressure in a way that encourages the horse to perform while ensuring the animal's welfare is prioritized.

These materials are also durable and can withstand the demands of rodeo activities, making them a practical choice for both the horse's comfort and the rigors of the sport. Other materials like silk, leather, or cotton may not provide the same level of comfort or protection, as they can lead to increased friction or wear against the horse's body, which might compromise its performance or lead to discomfort. Thus, fleece or neoprene is the optimal choice for lining a flank strap due to its combination of comfort, safety, and durability.